The present invention relates to a sheet cutter for cutting a sheet such as a paper sheet, and a plastic film, which is used in a printer or a ticket issue machine for cutting a roll sheet into a sheet having a predetermined length.
Such a sheet cutter has a fixed blade and a movable blade. Either of the fixed blade and the movable blade has an inverted V-shaped edge, and the other blade has a straight edge. The movable blade is elastically deformed during the moving thereof and elastically engaged with the fixed blade by the restitutive power of the deformed blade during the cutting operation so as to cut the sheet. For example, Japanese Patent Publications 8-22517 and 8-5030 and Japanese Utility Model Publication 7-11907 disclose such sheet cutters.
FIG. 25 shows the sheet cutter disclosed in the Japanese Patent Publication 8-22517.
A movable blade 61 made of quenched carbon tool steel has a chevron-shaped (inverted V-shaped) edge 61a and is slidably attached to a frame 62 so as to be moved in the vertical direction. A fixed blade 63 is pivotally supported on the frame 62 by opposite shafts 64. A lever 67 is secured to a side of the fixed blade 64. A lower end of the lever 67 is connected to an end of a spring 65, so that an edge 63a is pressed against the movable blade 61.
As shown in FIG. 26, the edge 63a of the fixed blade 63 is curved to the movable blade to form an arcuated edge. Thus, an inside corner edge of the arcuated edge 63a is pressed against the side surface of the edge 61a of the movable blade 61.
A paper sheet (not shown) is inserted into a window 66 from the back side of the cutter by a predetermined length. The movable blade 61 is lowered so that the paper sheet is cut from the opposite sides thereof and the cutting is finished at a central tip end portion of the blade 61. Since the fixed blade has the arcuated edge 63a, both blades cut the sheet in the same manner as the scissors.
The Japanese Patent Publication 8-22517 further discloses a cutter, a movable blade of which has a V-shaped edge. The Japanese Patent Publication 8-5030 and Utility Model Publication 7-11907 also disclose sheet cutters similar to that of the Publication 8-22517.
Each of these sheet cutters has a chevron-shaped blade edge or a V-shaped blade edge in order to ensure the contact between the slidable blade and the fixed blade during the cutting operation.
If each of the slidable blade and fixed blade has a straight edge, the whole surface of the edge does not contact with the edge of the other blade over the whole span of the edge, because of the warp or wave of the board of the blade. In case that a space is formed between edges of both the blades, the sheet cannot be entirely cut or is broken. In order to prevent such a defective cutting operation, one of the blade edge is formed into a chevron shape or a V-shape so as to effect the scissors operation.
However, in order to accurately form the V-shaped edge into an optimum shape, the manufacturing cost increases. On the other hand, in order to keep the contact between the movable blade and the fixed blade, the contact pressure is increased, the consumption electric power increases and the blades quickly wear.
If one of the blades is made of a flexible thin plate so as to remove the above described defects, the thin plate may be deformed when a thick sheet is cut. Furthermore, the contact pressure of the thin plate decreases as the cutting points move to the opposite sides of the blade. As a result, it may occur that the sheet cannot be entirely cut at opposite sides.